The Siemens 5SY4114-7CV is a 1-pole miniature circuit breaker (MCB) rated C0.3A with a breaking capacity of 15kA at 230/400V. That interrupting rating means it can safely clear a fault up to 15,000 amps without welding its contacts or rupturing the case — a spec that matters when the prospective short-circuit current at the panel is high, typical for industrial sub-distribution boards close to the transformer.
Snaps onto standard 35mm DIN rail per EN 60715. The C0.3A rating follows the C-curve characteristic (5-10x In magnetic trip), so it handles moderate inrush from small control transformers or solenoid loads without nuisance tripping, while still protecting the 0.3A branch circuit. Single-pole format fits a 1-module width (approx 18mm) on the rail.